Pot, at least certain amounts of it, will soon be legal under state laws in Washington. So it begs the question – how will law enforcement investigate DUIs where the suspect appears under the influence of marijuana?

First, Washington’s law does change DUI provisions by setting a new blood-test limit for marijuana – a limit police are training to enforce. Know this: they’re proactively going to arrest drivers who drive impaired, whether it be drugs or alcohol. Drugged driving is illegal, and nothing in the measures that Washington voters passed this month to tax and regulate the sale of pot for recreational use by adults over 21 changes that.

Statistics gathered for the National Highway Traffic Safety Administration showed that in 2009, a third of fatally injured drivers with known drug test results were positive for drugs other than alcohol. Among randomly stopped weekend nighttime drivers in 2007, more than 16 percent were positive for drugs. Studies also show that Marijuana can cause dizziness and slowed reaction time, and drivers are more likely to drift and swerve while they’re high.

Most convictions for drugged driving currently are based on police observations, followed later by a blood test. Unlike portable breath tests for alcohol, there’s no easily available way to determine whether someone is impaired from recent marijuana use.

According to the National Highway Traffic Safety Administration, peak THC concentrations are reached during the act of smoking. However, within three hours, they generally fall to less than 5 nanograms per milliliter of blood – the same standard in Washington’s law, one supporters describe as roughly equivalent to the .08 limit for alcohol.

In Washington, police still have to observe signs of impaired driving before pulling someone over. The blood would be drawn by a medical professional, and tests above 5 nanograms would automatically subject the driver to a DUI conviction.

My opinion? Simply put, people arrested for DUI should ready themselves to get transported to the hospital for blood testing. I believe officers will take defendants to the hospital if they appear AT ALL impaired; whether it be drugs or alcohol. I also predict that law enforcement is going to be concerned about people consuming a combination of alcohol and marijuana. Perhaps people will believe they can consume one or two drinks – enough to stay under the .08 limit – and follow it up with smoking marijuana to maintain the “high” of being under the influence. The slight combination, some may believe; may mask any signs they are under the influence of alcohol, especially if the alcohol consumptions signs are minimal.

Don’t think you can fool ’em. Believe me, the hospitals will become more crowded with drug-DUI investigations. And if people refuse the blood test, it’s just like refusing a BAC test: raised penalties and heavier DOL consequences.